As portable electronic devices, micro-electromechanical systems (MEMS), and smart cards become smaller and thinner, so too must the integrated circuits from which they are fabricated. Thin circuits not only consume less space, they also allow for more functionality per unit volume, increase power dissipation, and provide for a mechanically flexible device that may conform to curved surfaces. Thin circuits are typically fabricated on ultra-thin substrates, such as ultra-thin silicon wafers. Typical dimensions of ultra-thin wafers are about 60 μm to 80 μm, while the theoretical limit for suitable thin wafers is about 10 μm.
Bernoulli end effectors have been used in various applications to handle thin substrates. Bernoulli end effectors use a support member with fluid exhaust ports brought into close proximity with the top side of a substrate. The exhaust ports are configured so that the gas flow creates a low pressure region on the top side of the substrate causing it to lift up toward the support member. The substrate can be lifted from a substantially flat surface and transported from the top side of the substrate without contacting the top side. Contacting a semiconductor wafer during processing typically contaminates it, thus decreasing the yield from individual semiconductor wafers.
A disadvantage of many prior art Bernoulli end effectors is that they do not provide guides to position the substrate, and thus do not provide for high precision centering of the substrate. Another disadvantage is that the holding mechanism restricts the transport motion to paths within a horizontal plane or perpendicular to a horizontal plane.
Disadvantages of thin substrates include processing difficulties, such as cracking, bowing, or flexing during lifting, holding, handling, and transporting the substrates. Bernoulli end effectors can transfer thin substrates, but many substrate cassettes and assembly area tools cannot accommodate them. Further, a method for processing both sides of a substrate is desirable, but supinating or flipping a substrate is difficult.